1. Field of the Invention
The present invention provides a method and apparatus for generating multiple phase shifted clocks using a series of delayed clocks. A phase shifted clock can be used to generate a DVD write power control waveform with high precision.
In writing data to a DVD (Digital Video Disk) disc, a number of series of pulses may be required in order to accurately write data to the disc. T is 1 full EFM (eight-to-fourteen Modulation) clock cycle. Very fine resolutions of ⅛T, 1/16T, 1/32T are needed to generate proper power control waveform.
Prior art U.S. Pat. No. 6,775,217 uses analog ring oscillator FIG. 1 to generate an eight phase clock at 4× EFM clock. This prior art needs an analog design, which requires a large circuit size, and is limited in speed.
It is therefore an object of the invention to use digital delay cells to generate multiple phase shifted clocks.
It is another object of the invention to use digital delay to generate multiple phase shifted clocks using only 1× EFM clock to avoid the need for high speed processing.
It is another object of the invention to allow the use of smaller die sizes by using digital design.
It is another object of the invention to consume less power by avoiding use of analog design.